ASA 125th Meeting Ottawa 1993 May

1pPA6. Ultrasonic measurements of excess nonlinearity in polymers.

Laszlo Adler

Peter B. Nagy

Dept. of Welding Eng., Ohio State Univ., Columbus, OH 43210

To obtain nonlinearity parameters of solids one may use either harmonic
generation of finite amplitude waves or the stress dependence of the sound
velocity, the so-called acoustoelastic effect. In strongly viscoelastic
materials, e.g., in polymers, both linear and nonlinear responses are
significantly time-dependent and the quasistatic acoustoelastic effect is
relatively much stronger than the dynamic harmonic generation effect. In this
presentation, several modifications of the acoustoelastic method will be
introduced in order to study the effect of excess nonlinearity in polymers due
to fatiguing. An experimental system was developed where external bending load
was used to degrade polymeric bars through fatigue and simultaneously monitor
nonlinearity via the acoustoelastic effect. Due to the symmetry of the applied
bending load, only the second-order nonlinearity (combination of second-,
third-, and third-order elastic constants) was measured. It was demonstrated
that for thin layers, such as adhesive bonds, a different acoustoelastic effect
can be observed by measuring the stress dependence of the attenuation
coefficient.